just in one of the 2 principal characters by whieli that genus is distinguished 

 from Monsttilla, viz., in the number of caudal setae. Both according to the 

 description given by Kr0yer in "Naturhistorisk Tidsskrift" and to the figures in the 

 Atlas to Gaimards voyage, the caudal rami in Kreyers species are each provided 

 with 5 well-developed setae, as in most species of the genus Monstrilla, whereas 

 in Giesbrecht's genus the number of. setae is much reduced, only 3 such setae 

 occuring on each ramus (at last in female). In any case, if it should be 

 found advisable to support the genus Thaunialens of Kreyer, it must be 

 confined to the species recorded by that author. Fortunately we have another 

 generic name to replace that given by Giesbrecht to his genus, viz., 

 Cymbasoma, proposed as early as the year 1888 by I. C. Thompson for 

 a species (rigidum), which evidently is referable to Giesbrecht's genus. The 

 genus Hcemocera of Malaquin I regard as synonymous with that genus. In 

 addition to the 2 genera Monstrilla and Cymbasoma, I have found it advisable 

 to establish another genus, Moiistrillopsis, to include the anomalous species 

 described by Scott under the name of Monstrilla dubia. The family Monstrillidae 

 thus at present comprises 3 genera, all of which are represented in the fauna 

 of Norway. 



Though I have not myself as yet had any opportunity to study the 

 peculiar life-history of the Monstrillida?, I think that a short resume" of the 

 interesting investigations made in this respect by the French naturalist Malaquin 1 ) 

 may here be given. According to that distinguished author, the young live 

 the eggs as small Nauplii, without mouth or alimentary canal, but provided 

 in front with the usual 2 pairs of limbs (anterior and posterior antennae) and 

 behind them on each side with a hook-like appendage (mandibles). The Nauplii 

 soon attach themselves to some polychaete Annelid and penetrate through the 

 body-wall of the same, then entering the vascular system. By this process 

 they lose completely all their appendages, and become converted to simple 

 ovoid bodies merely consisting of an assemblage of indifferent embryonic 

 cells surrounded by a thin cuticle. From the one end of these bodies 2 soft 

 horn-like processes grow out, gradually increasing in length, and at last assuming 

 the form of slender thread-like appendages. It is supposed that through these 

 appendages the absorbtion of the blood-serum of the host is performed, and 

 according to their position they may answer to the posterior antenna?. During 

 the rapid growth of these endo-parasitic larvae a remarkable differentiation take 

 place in their interior, resulting in the formation of the characteristic and rather 



';. See: Arch. Zool. Exp. (3), Vol. 9, 1901. 



2 Crustacea. 



